One of the methods of driving a synchronous motor (hereinafter simply called as motor) is to employ position sensor for sensing the magnetic pole position of rotor. Position sensor in this description means ones including resolver or absolute encoder that cannot only sense the rotating angle in rotation but also determine the absolute position in standing. In order to drive a motor efficiently, however, matching the position sensor with the counter electromotive voltage (magnetic pole position of the motor rotor) very much accurately is inevitable, and several methods for it have been disclosed.
Japanese Patent Laid-Open No. Hei 09 (1997)-56199 discloses a technique where the voltage and current applied to the armature coil are sensed and the magnetic pole position of the rotor is estimated, and then the shift of position is sensed from the error between the rotating position sensed by the position sensor and the pole position, and the shift is corrected accordingly.
Japanese Patent Laid-Open No. Hei 10 (1998)-80188 discloses a technique where the magnetic pole position is estimated from the motor current and drive voltage, motor constant and certain speed, and the mounting error of the position sensor is corrected accordingly.
Japanese Patent Laid-Open No. 2000-102299 discloses a technique where the drive is equipped with a position estimating means that estimates the phase difference Δθ between the reference position of the rotor of a synchronous motor and the reference position of the position sensor only from the sensed motor current, and the phase difference of the position sensor is corrected accordingly.
Japanese Patent Laid-Open No. 2001-251889 discloses a formula for estimating the shift of axis in sensorless control.